Hydraulic couplings



1963 A. CROFT ETAL 3,107,492

HYDRAULIC COUPLINGS Filed Aug; 20, 1959 2 Sheets-Sheet 2 United States Patent 3,107,492 HYDRAULIC COUPLINGS Arthur Croft, Rawdon, Maurice T. J. G'oir, Bingley, and Frederick 0. Ackroyd, Idle, England, assignors to Crofts (Engineers) Limited, Thornhury, England, a company of Great Britain Filed Aug. 20, 1959, Ser. No. 83:5,(962 Claims priority, application Great Britain Aug. 25, 1958 4 Claims. (Cl. 60-54) This invention relates to hydraulic couplings of the kinetic type, embodying internally vaned elements arranged as an impeller and a runner, which together define the boundary of an annular working chamber in which, under torque-transmitting conditions, liquid circulates in the form of an annular vortex to transmit torque from the impeller to the runner.

Such couplings have been known for many years in varied forms. The classic form of Vulcan coupling, developed from Fottinger designs, employed in the annular working chamber a core guide ring arrangement around which the liquid vortex was caused to circulate during torque-transmitting conditions.

It was realised at an early stage in development that variations in quantity of liquid in the working circuit would produce corresponding variations in the performance of the coupling, not only because they afiect the drag or slip under conditions when the runner is stalled whilst the impeller is being driven, but also because the quantity of liquid in circuit at any given time determines the amount of torque capable of being transmitted by the particular size of coupling concerned.

For the above reasons, means for varying the degree of filling of hydraulic couplings have long been known. In some cases, the coupling has been emptied by simple draining methods, and refilled by pump. In other cases, scoop tubes or similar devices have been used in conjunction with an external reservoir for varying the amount of liquid in the working chamber.

In later years, and particularly for industrial purposes, e.g. for driving machinery from a squirrel-cage induction motor, the rotary reservoir type of coupling has been developed. In this type of coupling a reservoir is formed between the back of the runner and a rotary casing attached to the impeller. The rotary reservoir communicates with the working chamber at its inner and outer peripheries through the normal clearance space or gap between the impeller or runner, and at least the outer part of the reservoir communicating with the working chamber at its outer periphery is of suitably tapered or constructed form in radial section so that return of liquid from the reservoir to the working chamber is speeded up as slip decreases and, under normal torque-transmitting conditions, a balance is achieved between the amount of liquid in vortex circulation in the working chamber and the amount of liquid in the radially outer part of the reservoir. Filling of the coupling with liquid is limited so that, under normal working conditions, there is an air space at the radially inner part of the reservoir available to receive liquid from the working chamber as slip increases, this air space being as near as possible to the axis of the coupling to reduce to a minimum back pressure resulting from centrifugal action built up in the reservoir on the liquid forced out of the working chamber. Thus, the rotary reservoir acts to reduce the amount of liquid in the working chamber and hence the torque transmitted when the runner is stalled, and to return liquid to the working chamber by the action of centrifugal force when the runner speeds up and slip is reduced. Moreover, a rotary reservoir type coupling can be filled to varying degrees to enable any given size of coupling to possess a predetermined torque-limiting capacity at stall.

In this way, a single size of coupling may be supplied, able to give varying degrees of maximum torque according to the degree of filling which is specified, so that the customer can himself limit the torque to be transmitted, and vary that limit if necessary.

The present invention is specifically concerned with improvements in couplings of the rotary reservoir type particularly suitable for industrial use, as above referred to.

Hydraulic couplings employed for industrial purposes have to satisfy the following requirements:

(a) Low slip at normal operating speeds and torques,

lying within the designed limits of the couplings; (b) Low drag torque, at low speeds of the impeller, when the runner is stalled; (0) Rapid pick-up of runner speed, i.e. rapid reduction of slip during the acceleration range of the runner from stall to drive conditions; (d) Torque limitation at high slip, i.e. high speed difference between impeller and runner, e.g. to prevent overload of the driving motor and/ or driven machine as occurs when the runner is stalled suddenly.

The above requirements differ somewhat from those desired in couplings for automotive purposes in which, in particular, full engine torque is required especially at starting and requirement (d) would be detrimental.

To a great extent in conventional designs of coupling, requirement (a) is satisfied by the provision of the maximum number of driving vanes in the impeller and runner, within recognized limits. However, any increase in the number of vanes will normally tend to increase the stall torque, i.e. the torque transmitting capacity of the coupling under stall conditions (herein called the stall torque capacity) that is, when the runner is stalled and the impeller is driven at or near normal speed, and this consideration has, in the past, imposed an upper limit on the number of driving vanes in any given size of coupling.

Requirements (b) and (c) are generally satisfied by the automatic functioning of the rotary reservoir. Requirement (d) has been met in several ways. As already explained, fewer driving vanes results in less torque under any conditions, but this is not a satisfactory solution as it affects efiiciency at normal operation speeds and torques. Again, reduction in the quantity of liquid in the working circuit can reduce drag torque, and in variable content couplings, many designs have aimed at emptying the coupling during the period when the runner is stalled. However, in cases where variable content couplings are used, undesirable fluctuations and surges in torque can appear.

It was found by Sinclair, as explained in his British Patent No. 384,022, that the introduction of a deflector protruding from the wall of the working chamber into the boundary of the working circuit, had the effect of reducing stall torque in partly filled couplings without introducing the undesirable fluctuations and surges referred to. Sinclair explained that the deflector had the efieot of breaking up the shallow high speed vortex which tends to form around the outer periphery of the working circuit nearest the walls of the chamber, under conditions of high slip. Considerations of manufacturing convenience have led to the widespread use of a fiat discshaped bafiie (herein called a baffle disc) located in the plane of rotation of the coupling, and at the junction of the impeller and runner, and fixed to one or other of these members.

During the period of these developments which covered some 25 to 30 years from 1905, when the original Fottinger hydraulic coupling was invented, it was ap preciated that centrifugal forces resulting from high speed rotation of the coupling tend to cause the vortex to distort, because all the liquid in the vortex is being urged towards the periphery of the coupling. Thus, there is a tendency, under these conditions, for that part of the vortex on the innermost region of the circuit to move away from the walls of the chamber nearest the axis of rotation of the coupling, so that the vortex boundary becomes flattened in this region. It was also appreciated that this tendency of the vortex to distort brought to light disadvantages in the :use of a core guide ring because the center of rotation of the vortex is not constant and tends to move towards the outer periphery of the coupling at high coupling speeds. In such circumstances the core guide ring no longer remains substantially concentric with the vortex, and thus it was realized that a core guide ring might well be interfering with the vortex flow and artificially diverting that flow in the region where the vortex is attempting to flatten itself, thus reducing efficiency at normal load.

Proposals were therefore made from time to time to omit the core guide ring, thereby providing what is now generally known as an open circuit coupling.

In an open circuit coupling the vortex formed under normal working conditions tends to assume a flattened formation and to be concentrated in a radially outer part of the working chamber, while, on the occurrence of high slip, e.g. at stall, the vortex speeds up and expands into a shallow formation conforming substantially to the inner boundary wall of the working chamber and traversing the radially inner part thereof.

One of the most significant moves in this direction was evidenced by some of the designs employed by the Daimler and Lanchester Companies for their traction coupling (commonly termed a fluid flywheel), which largely followed Sinclair designs, and which dispensed with a core guide ring in the working chamber. This structure, however, had no deflector but it did possess an increased number of vanes as compared with other current designs of traction couplings.

However, in British Patent No. 470,774, Sinclair discussed some difliculties introduced by the omission of a core guide ring in a variable content coupling, mentioning, in particular, the instability of torque transmission at certain degrees of filling, and suggested, as a solution for the instability, providing on the impeller at least one annular guide member in the form of a vane disposed coaxially with the coupling and located in a position in the path of the liquid stream from the runner to the impeller, where it would tend to guide that stream rapidly and smoothly towards the impeller vanes. It was pointed out that such a guide vane would act as a barrier which would reduce the rate of distortion of the vortex under conditions of acceleration and deceleration of the coupling, land would consequently reduce the tendency to instability in torque transmission over this range of coupling speeds.

British Patent No. 470,774 also suggested the combination of an open circuit with a bafile disc deflector of the conventional form to reduce torque at high slip.

The use of such a baffle disc in an open circuit coupling operating in a partly filled condition, revealed a further significant advantage. Whilst the bafile disc is effective as a deflector under stall conditions to reduce the torque transmitted, it rapidly loses its effectiveness as the coupling speeds up. This appears to be due to the tendency for the vortex to flatten at its innermost region, and in doing so, move away from the baflle which gradually emerges from the liquid until finally the battle is quite clear of the vortex. Such behaviour of the vortex is consistent with observed results, namely, a progressive reduction in the effectiveness of the battle and a corresponding progressive increase in the torque transmitted over the acceleration range of the runner which is highly desirable.

In British Patent No. 538,043, Sinclair disclosed an automotive coupling which has come to be known as the Vulcan Sinclair traction coupling. This, as made and sold for industrial purposes, possesses three features in combination. The first feature is a completely open circuit, omitting both the core guide ring and also the guide vanes of British Patent No. 470,774. The second feature is the use of an increased number of vanes as compared with previous constructions of Vulcan Coupling, whilst the third feature is the use of a bafiie of considerably larger size than had previously been thought desirable. Additionally, in the practical commercial form, this coupling employs a rotary reservoir as above described which acts to vary the contents of the Working circuit automatically under working conditions. This Vulcan Sinclair coupling was shown to be considerably more efficient than the previous Vulcan coupling which had employed a core ring and which did not normally employ a bat-fie.

Apparently the use of an open circuit enables the vortex in a partly filled coupling to distort to a greater extent than was possible when the interference of a core guide ring was present. It seems that the boundary of the vortex under normal torque-transmitting conditions lies further from the axis of rotation of the coupling than is the case where a core guide ring is provided, so that the increase in the diameter of the bafile disc has no adverse effect on normal torque transmission, whilst giving beneficial results under stall torque conditions. As a result, the number of vanes may be increased with boneficial effect on slip under normal torque-transmitting conditions without increasing the stall torque to an unacceptable degree.

However, Sinclair found, as he states in his later British Patent No. 669,331, that with a coupling of the type described in British Patent No. 538,043, there is an unsatisfactory spacing of the torque-slip curves relating respectively to various degrees of filling, and that if such a coupling is operated in the pantly filled condition, the speed characteristic is poor owing to the flatness of the torque-slip curves.

Another feature in all the previously mentioned patent specifications and in couplings generally is that at least some of the radial vanes in the working chamber extend to the chamber boundary wall of the innermost region with any remaining vanes extending substantially into such region. Thus, there are vanes which coact with the working fluid in the innermost region of the working chamber.

It has now been found that the above-mentioned requirements for couplings employed for industrial purposes can be met in a hydraulic coupling of the rotary reservoir open-circuit type without the employment of baffles or deflectors in the working circuit. In addition, all the tests carried out to date seem to indicate that with such a coupling it is possible to vary the stall torque of the coupling over a range greater than can be achieved by previous designs of coupling and Without significant loss of overall efficiency merely by variation of liquid filling.

A hydraulic coupling of the rotary reservoir type according to the present invention has a working chamber which is free of core guide rings or other guide means so as to provide an open circuit; the boundary wall of the working chamber is of smooth toroidal form without baffies, pockets or other means for interrupting the fiow of the shallow high speed expanded vortex which develops under conditions of high slip or stall, and between the vanes on the impeller and the vanes on the runner, a free space is provided at the radially inner part of the working chamber in the path of said shallow expanded vortex, said free space being of such size and so arranged that the maximum value of the torque-transmitting capacity of the coupling under predetermined conditions of stall, does not exceed a desired multiple of the torque-transmitting capacity of the coupling under conditions of normal slip,

Volume of Free Space/Volume of Total Capacity Working Circuit Up to 1,000 cu. ins 1,000 to 4,000 cu. ins

As slip increases from normal up to stall, the liquid vortex in the Working chamber tends to expand so that part of it traverses the free space in which the liquid is neither receiving energy from the impeller nor transmitting it to the runner, and at the same time this expansion of the vortex tends to force liquid out of the working circuit into the reservoir. The volume of the free space in relation to the volume of the working circuit within the ranges indicated, therefore, is a factor affecting the ratio of stall torque to torque at normal slip. The size and shape of the Working circuit and the rotary reservoir and the number of vanes is calculated and designed according to well-known practice in hydraulic couplings of the rotary reservoir type. In particular, the volume of the reservoir in relation to the volume of the Working chamber is made sufficiently large to accommodate displacement of liquid from the working chamber to ensure the formation of a shallow high speed expanded vortex under conditions of high slip. We have found that the volume of the rotary reservoir preferably should be in the region of to of the total capacity of the coupling, as set out in the following Table B.

Volume of Res- Total Capacity ervoirl'lotal Capacity Up to 1,000 cu. ins %n to %9 1,000 to 4,000 cu. ins e to %9 The free space preferably is formed by omitting a radially inner part of the vanes of both the impeller and the runner so that all the vanes in the working chamber terminate a predetermined distance short of the radially inner boundary wall of the working chamber to form a free space extending substantially symmetrically within the impeller and the runner and defined by the inner edges of the vanes and the inner boundary wall of the working chamber. This symmetrical arrangement of the free space is preferred as the effect on torque transmission from the impeller to the fluid will be the same as from the fluid to the runner and vice versa, so that the input and the output shafts are reversible in function. If desired, the free space may be asymmetrically arranged so that a greater part, or the whole, thereof is located in the impeller or in the runner.

Experiments have shown that couplings having volumetric relationships as above defined effectively pro vide the required characteristics for industrial use, being capable of operating at high efliciency during normal torque transmitting conditions, i.e. at low slip, while providing for low drag torque When the runner is stalled at low impeller speeds, a desired torque limitation at high slip when the runner is stalled at high impeller speeds, and rapid reduction of slip during acceleration of the runner from stall to normal driving conditions, these results being obtained with a very simple construction of coupling without core guide rings or deflectors or baffles, r scoop and pump, or other relatively complicated means for effecting transference of liquid to and from the working chamber. Tests have shown that the reduction in vane area to form the free space does not adversely alfect the coupling efficiency under normal torquenansmitting conditions since, with decrease in slip, the liquid vortex flattens at its innermost region and moves away from the free space.

Various tests have shown good results under stall torque conditions. It would appear that liquid flowing radially inward from between the vanes in the runner enters the free space where kinetic energy still remaining in the liquid becomes substantially ineffective to transfer energy from the impeller to the runner so that the desired reduction in stall torque and also low drag torque at low impeller speeds can be achieved.

Dependent on the degree of filling of the coupling up to the maximum permissible limit Otf an 8 to 1 ratio between the volume of liquid and the volume of air space left in the coupling, the stall torque in the coupling according to the invention will be reduced from to 600% of the torque-transmitting capacity at normal slip as compared with a stall torque of from 1600% to 1700% usual in previously known couplings, while at the same time an efliciency of the order of 5% to 6% slip under conditions of normal torque transmission is obtainable. When the coupling is driven by a motor power-matched with the coupling rating, by using the appropriate oil filling, the stall torque can be reduced to match the characteristics of the motor to protect both motor and driven machine. The higher stall torque ranges obtained with the appropriate oil filling is advantageous where starting torque requirements are much greater than the running torque requirements.

The invention is hereinafter described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is a vertical half-section illustrating one embodiment of hydraulic coupling according to the invention;

FIG. 2 is a chart giving preferred volumetric relationships in a specified range of coupling sizes;

FIG. 3 is a half-section of a coupling according to the invention showing a modified construction of the radial wanes;

FIG. 4 is a view similar to FIG. 3 illustrating a further modification; and

FIG. 5 is a half-section illustrating the application of the invention to a coupling of the tandem type.

In carrying the invention into effect, and with reference to FIG. 1 of the accompanying diagrammatic drawings, a hydraulic coupling of the rotary reservoir type includes an impeller 1 and a runner 2 which, together, provide an annular working chamber 3 in which radial vanes 1a, 2a are disposed. A reservoir 4 is provided by the space between the back of the runner 2 and the rotary casing 5 attached to the impeller 1, with a relatively narrow annular gap 6 at the peripheral edge of the runner for working liquid to flow automatically from the chamber '3 between the opposing faces of the impeller and runner into the reservoir 4 land to return therefrom into the working chamber according to working conditions. Any air space, such as 4a, behind the coupling bearing 11 is included in the capacity of the reservoir. This coupling construction and arrangement is substantially conventional other than in regard to the radial vanes 1a, 2a, and the volumetric relationships as hereinafter described.

The inner edges 7 of all the radial vanes 1a, 2a may be inclined, curved or otherwise suitably shaped and terminate short of the inner part 8 of the chamber boundary wall of the innermost region of the chamber to provide a free space 9 having a definite volumetric relationship with respect to the total volume of the working chamber 3. The free space 9' is, in effect, bounded by the vane edges 7 and the boundary Wall 8 of the impeller and runner in the innermost region.

The free space 9 forms a region into which liquid flows during conditions of increasing slip up to maximum 7 slip and Under stall conditions, whereby the kinetic energy still remaining in the working liquid in the runner flowing inward between the radial vanes 2a and passing their inner edges 7 into the free space 9, becomes substantially ineffective for torque transmission to the runner since the radial vanes of the runner do not extend into the free space.

Furthermore, no energy is given to the liquid within the free space by the vanes 1a of the impeller which do not extend into the free space. Thus, the total torque transmission from the impeller to the runner under high slip or stall conditions is reduced to a desired amount.

In order that the free space can perform its function, the volume of the reservoir should be suitably related to the volume of the working chamber so that under stall conditions, liquid will be displaced from the Working chamber into the reservoir to allow the development of the shallow high speed expanded vortex conforming to the boundary wall of the working chamber. In the chart shown in FIG. 2, it will be seen that the optimum volumetric relationships over a number of coupling sizes vary within a somewhat limited range. In the chart, TC: total capacity; VWC:volume of the Working chamber; VR=volume of the reservoir, and VFS=volume of the free space. It will be seen also that VWC/TC ranges from to 9 VR/TC ranges from 9 to and VFS/VWC ranges from 5 to & It will be understood that the limited ranges indicated are given only by way of example of preferred volumetric relationships which have been found to give the coupling the desired characteristics. Obviously, for particular applications, e.g. when using a matched motor, a desired limitation of stall torque within the range specified could be achieved with volumetric relationships outside the limited ranges given in the chart.

In a specific example, the size 4 coupling is designed to operate at 6.3 H.P. at 1450 r.p.m. From this data the dimensions of the annular working chamber 3 are calculated giving an outer diameter of 9.5 inches, an inner diameter of 3 inches, and a width of 2.875 inches, these dimensions giving a calculated volume VWC of 127 cubic inches. From the volumetric relationship VWC/TC, the total capacity is found to be approximately 184 cubic inches and therefore, the total volume of the reservoir, including any additional space such as 4a, must be TC-VWC=57 cubic inches. The volume of the free space VFS, being of the volume of the working chamber, will be 22 cubic inches. This free space may be formed by arranging the edges 7 of the vanes 1a and 2a to have an inclination of about 30 from a line A parallel with the axis of the coupling and at a radius of 2.75 inches from the axis of the coupling. Within the limits prescribed by its volumetric capacity, the reservoir is designed in the manner customary in rotary reservoir type couplings so that the air space left in the reservoir when the coupling is operating under normal torquetransmitting conditions, is located as near as possible to the axis of the coupling, and so that transference of liquid from the reservoir to the working chamber is speeded up as slip increases. Such a coupling may have, say, 45 vanes in the impeller and 42 vanes in the runner, although these numbers may be varied within predetermined limits for given requirements. The said vanes have equal spacing in their respective elements and the small variation between them avoids the possibility of masking during running. Alternatively, sets of vanes with graduated vane spacing of known form may be used, provided that none of the vanes extends into the free space.

Under normal driving conditions, when the coupling is rotating at normal slip, displacement of liquid from the vortex in the working chamber 3 through the gap 6 is prevented by a body of liquid held in the outer part of the reservoir by the action of centrifugal force. Under these conditions, the coupling operates at normal ratings at high efliciency. Under conditions of high slip, or when the runner is stalled, liquid is displaced from the working chamber into the reservoir. The air space left in the radially inner part of the reservoir when operating under normal low slip conditions, combined with the volume of the free space 9, is so related to the total volume of the working chamber 3 that, under conditions of high slip, e.g. under high speed stall conditions, the liquid remaining in vortex circulation in the chamber 3 is reduced to a suitable amount so that the function of the free space enables the stall torque to be reduced to to 600% of the torque-transmitting energy at normal slip dependent on the degree of liquid filling and the driving torque applied to the coupling.

The amount of air space in the coupling depends on the degree of filling. At maximum, or 0 filling, wherein the ratio of volume of liquid to volume of air space left in the coupling is not more than 8 to l, which is known to be the approximate limit above which dangerous internal pressures become possible due to expansion of the liquid air ratio if the coupling heats up due to prolonged stalling, the volume occupied by the liquid will be ap proximately cubic inches, leaving an air space of about 24 cubic inches. Maximum filling of the coupling to the above ratio is obtained when a suitably disposed overflow outlet is at 0, i.e. perpendicularly above the axis of rotation of the coupling. Minimum filling is at a level determined by disposing an outlet at 70 from the pcrpendicular and within these limits the filling of the coupling may be varied according to requirements to place any desired limitation on the stall torque of the couping.

The free space 9 may be formed by any other suitable shaping of the vanes 1a, 2a. For example, as shown in FIGS. 3 and 4, the edges 7a, 7b respectively of the vanes 1a, 2a may be uniformly shaped to curved or other formation to give a free space 9 which is symmetrically disposed with respect to the impeller and the runner. If desired, however, the free space may be asymmetrically arranged as before mentioned. In certain circumstances, the vanes need not be of uniform length but may have a given number of greater, or part greater, length than the remainder but all terminating within a predetermined innermost limit defining the effective free space 9.

As shown in FIG. 5, the invention is applicable to a coupling of the tandem type in which, for example, two oppositely facing impellers 1b, 1c co-operate with axially spaced runners 2b, 20 mounted on a common output shaft 12. The rotary reservoirs 5b, 5c and the impellers 1b, 10 form a unitary structure which is coupled to an input shaft 13. In accordance with the invention, each section of the coupling is constructed, as before described, to provide a free space 9a at the radially inner part of the working chamber and with the volumetric relationships between V-FS, VWC and VR such as previously described.

The significant novel features of this invention include (1) in a rotary reservoir type of coupling; (2) a novel and critically important shape of the rotary casing 5 (reservoir 4), illustrated in FIGS. 1 and 5; (3) specifically described and claimed volumetric capacities of free space 9, FIGS. 1, 3, 4 and 5, and working chamber 3; (4) no use of pressurization at any stage of the working cycle; (5) specifically described and illustrated free space 9, wherein none of the vanes 1a or 2a, FIG. 1, for example, or any parts thereof extend into this space.

It will be understood that couplings constructed in accordance with the invention as above described may be modified in various respects according to working requirements. Furthermore, the couplings can be used for a variety of purposes and incorporate driving means, such as a pulley, mechanical drive coupling, or other means.

What we claim is:

1. A hydraulic traction coupling of the rotary reservoir type comprising an input shaft, an impeller connected to said input shaft for rotation therewith, an output shaft, a runner connected to said output shaft, said runner and said impeller defining an annular working chamber coaxially arranged relative to said output shaft, said runner and said impeller each having vanes in said working chamber, and a rotary casing connected to said impeller for rotation therewith, said runner and said rotary casing defining an annular reservoir chamber, said reservoir chamber being in communication with said working chamber by means of an annular gap intermediate said impeller and said runner, said annular gap being adjacent the radially outermost portion of said working chamber and said reservoir chamber being of gradually tapered form in rotary section so that return of liquid from the reservoir chamber to the working chamber is speeded up as slip decreases and, under normal torque-transmitting conditions, a balance is achieved between the amount of liquid in vortex circulation in the working chamber andthe amount of liquid in the radially outer part of the reservoir chamber, said vanes of said impeller and said runner extending radially inwardly from the radially outermost portion of said working chamber and all of said vanes termimating at their radially innermost edges a spaced distance from the radially inner boundary wall of said working chamber to define an uninterrupted annular free space, the volume of said annular free space being within the range of to of the total volume of said working chamber, and the volume of said reservoir chamber being Within the range of to 7 of the total capacity of the hydraulic coupling, whereby transfer of liquid between the working chamber and the reservoir chamber is automatically controlled Without the use of scoops, gas pressurizing or other extraneous means, so that the torquetransmitting capacity of the coupling under predetermined conditions of stall does not exceed a desired multiple of the torque-transmitting capacity of the coupling under conditions of normal slip.

2. Apparatus as defined in claim 1 wherein the boundary wall of said working chamber is of smooth toroidal configuration to cause the flow of the shallow high speed expanded vortex which develops under conditions of high slip or stall to be uninterrupted.

'3. Apparatus as defined in claim 2 wherein the volume of said annular free space is within the range of to V of the total volume of said working chamber.

4. A tandem type hydraulic traction coupling comprising an input shaft, first and second impellers and first and second rotary casings connected to said input shaftfor rotation therewith, an output shaft, and first and second runners connected to said output shaft for rotation therewith, said first impeller and said first runner defining a first annular working chamber and said second impeller and said second runner defining a second annular working chamber, said runners and said impellers each having vanes in their respective working chambers, said first runner and said first rotary casing defining a first annular reservoir chamber and said second runner and said second rotary casing defining a second annular reservoir chamber, said first reservoir chamber being in communication with said first working chamber and said second reservoir chamber being in communication with said second working chamber by means of annular gaps intermediate their associated impellers and runners, said annular gaps being adjacent the radially outermost portions of the associated working chambers and said reservoir chambers each being of suitably tapered form in radial section so that return of liquid from the reservoir chambers to the working chambers is speeded up as slip decreases and, under normal torque-transmitting conditions, a balance is achieved between the amount of liquid in vortex circulation in the working chambers and the amount of liquid in the radially outer part of the reservoir chambers, said vanes of said impellers and said runners of each of said working chambers extending radially inwardly from the radially outermost portion of said working chamber and all of said vanes terminating at their radially innermost edges a spaced distance from the radially inner boundary wall of said Working chamber to define an uninterrupted annular free space, the volume of said annular free space being within the range of 7 to of the total volume of said working chamber, and the volume of said reservoir chamber being within the range of $5 to of the total capacity of the hydraulic coupling, whereby transfer of liquid between the working chamber and the respective reservoir chamber is automatically controlled without the use of scoops, gas pressurizing or other extraneous means, so that the torque-transmitting capacity of the coupling under predetermined conditions of stall does not exceed a desired multiple of the torque-transmitting capacity of the coupling under conditions of normal slip.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A HYDRAULIC TRACTION COUPLING OF THE ROTARY RESERVOIR TYPE COMPRISING AN INPUT SHAFT, AN IMPELLER CONNECTED TO SAID INPUT SHAFT FOR ROTATION THEREWITH, AN OUTPUT SHAFT, A RUNNER CONNECTED TO SAID OUTPUT SHAFT, SAID RUNNER AND SAID IMPELLER DEFINING AN ANNULAR WORKING CHAMBER COAXIALLY ARRANGED RELATIVE TO SAID OUTPUT SHAFT, SAID RUNNER AND SAID IMPLELLER EACH HAVING VANES IN SAID WORKING CHAMBER, AND A ROTARY CASING CONNECTED TO SAID IMPELLER FOR ROTATION THEREWITH, SAID RUNNER AND SAID ROTARY CASING DEFINING AN ANNULAR RESERVOIR CHAMBER, SAID RESERVOIR CHAMBER BEING IN COMMUNICATION WITH SAID WORKING CHAMBER BY MEANS OF AN ANNULAR GAP INTERMEDIATE SAID IMPELLER AND SAID RUNNER, SAID ANNULAR GAP BEING ADJACENT THE RADIALLY OUTERMOST PORTION OF SAID WORKING CHAMBER AND SAID RESERVOIR CHAMBER BEING OF GRADUALLY TAPERED FROM IN ROTARY SECTION SO THAT RETURN OF LIQUID FROM THE RESERVOIR CHAMBER TO THE WORKING CHAMBER IS SPEED UP AS SLIP DECREASES AND, UNDER NORMAL TORQUE-TRANSMITTING CONDITIONS, A BALANCE IS ACHIEVED BETWEEN THE AMOUNT OF LIQUID IN VORTEX CIRCULATION IN THE WORKING CHAMBER AND THE AMOUNT OF LIQUID IN THE RADIALLY OUTER PART OF THE RESERVOIR CHAMBER, SAID VANES OF SAID IMPELLER AND SAID RUNNER EXTENDING RADIALLY INWARDLY FROM THE RADIALLY OUTERMOST PORTION OF SAID WORKING CHAMBER AND ALL OF SAID VANES TERMINATING AT THEIR RADIALLY INNERMOST EDGES A SPACED DISTANCE FROM THE RADIALLY INNER BOUNDARY WALL OF SAID WORKING CHAMBER TO DEFINE AN UNINTERRUPTED ANNULAR FREE SPACE, THE VOLUME OF SAID ANNULAR FREE SPACE BEING WITHIN THE RANGE OF 3/20 TO 7/20 OF THE TOTAL VOLUME OF SAID WORKING CHAMBER, AND THE VOLUME OF SAID RESERVOIR CHAMBER BEING WITHIN THE RANGE OF 8/29 TO 12/29 OF THE TOTAL CAPACITY OF THE HYDRAULIC COUPLING, WHEREBY TRANSFER OF LIQUID BETWEEN THE WORKING CHAMBER AND THE RESERVOIR CHAMBER IS AUTOMATICALLY CONTROLLED WITHOUT THE USE OF SCOOPS, GAS PRESSURIZING OR OTHER EXTRANEOUS MEANS, SO THAT THE TORQUETRANSMITTING CAPACITY OF THE COUPLING UNDER PREDETERMINED CONDITIONS OF STALL DOES NOT EXCEED A DESIRED MULTIPLE OF THE TORQUE-TRANSMITTING CAPACITY OF THE COUPLING UNDER CONDITIONS OF NORMAL SLIP. 